Body-Fat Calculator (Tape Method)
A tape measure and three numbers will give you a body-fat estimate. We’ve shown you the error bar alongside it, because without one this number is easy to take far more seriously than it deserves.
Your estimate
Estimated body fat
34.6%
from the circumference equations, using tape measurements only
Realistic margin
31.1–38.1%
these equations carry a standard error of about 3.5 percentage points
Treat this as a ballpark, not a measurement. Compared against DEXA scans in one study of Army recruits, these equations underestimated body fat by around six percentage points in both women and men, and the authors concluded circumference methods may not be an appropriate way to track changes in body composition over time. Use it to get oriented — not to judge whether a month of training worked.
A rough estimate for planning, not a diagnosis or medical advice. If you want a number you can actually track over time, a repeat measurement under identical conditions — or a scan — will serve you better, and your strength numbers better still.
What this is good for — and what it isn’t
Good for: getting oriented. If you have no idea whether you’re at 22% or 38%, a tape and these equations will land you in roughly the right neighbourhood for free, in about a minute.
Not good for: tracking progress. The equations carry a standard error of around 3.5 percentage points, and against DEXA scans in one study they underestimated body fat by roughly six points — with the authors concluding the method may not be appropriate for tracking change over time. A month of good training could easily be invisible inside that margin, or a month of nothing could look like progress.
So take the number, note that it’s a ballpark, and judge your progress with something steadier: a waist measurement taken the same way each time, or the reps and load in your training log.
Every estimate on this page has an error bar. Your training log doesn’t — either you lifted it or you didn’t. Mira tracks reps, load and form on every session, which makes it the one progress signal here you can trust week to week.
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